SSE3 explained

SSE3, Streaming SIMD Extensions 3, also known by its Intel code name Prescott New Instructions (PNI), is the third iteration of the SSE instruction set for the IA-32 (x86) architecture. Intel introduced SSE3 in early 2004 with the Prescott revision of their Pentium 4 CPU. In April 2005, AMD introduced a subset of SSE3 in revision E (Venice and San Diego) of their Athlon 64 CPUs. The earlier SIMD instruction sets on the x86 platform, from oldest to newest, are MMX, 3DNow! (developed by AMD, but not supported by Intel processors), SSE, and SSE2.

Changes

The most notable change is the capability to work horizontally in a register, as opposed to the more or less strictly vertical operation of all previous SSE instructions. More specifically, instructions to add and subtract the multiple values stored within a single register have been added. These instructions can be used to speed up the implementation of a number of DSP and 3D operations. There is also a new instruction to convert floating point values to integers without having to change the global rounding mode, thus avoiding costly pipeline stalls. Finally, the extension adds LDDQU, an alternative misaligned integer vector load that has better performance on NetBurst based platforms for loads that cross cacheline boundaries.

LDDQU — As stated above, this is an alternative misaligned integer vector load. It can be helpful for video compression tasks.

MOVDDUP, MOVSHDUP, MOVSLDUP — These are useful for complex numbers and wave calculation like sound.

FISTTP — Like the older x87 FISTP instruction, but ignores the floating point control register's rounding mode settings and uses the "chop" (truncate) mode instead. Allows omission of the expensive loading and re-loading of the control register in languages such as C where float-to-int conversion requires truncate behaviour by standard.